It is highly important to verify all the functions which a digital LSI circuit has in advance in order to avoid remanufacturing of the digital LSI circuit. It is therefore necessary to enumerate all the functions of the digital LSI circuit and verify each of the functions.
According to the present LSI design approach, however, since a manual process is employed to enumerate all the functions of a digital LSI circuit, it is impossible to prevent some functions from being omitted from the list.
Other than enumerating and verifying all the functions, the present LSI design process also uses other indexes for measuring the goodness of the verification. One of the other indexes is a toggle percentage. One example is disclosed in literature (D. Drako and P. Cohen, “HDL Verification Coverage,” Integrated System Design Magazine, pp. 46-52, June 1998).
The toggle percentage refers to the rate of change of signals at the time the circuit operation is finished, and is specifically determined as (L+H)2N where L represents the number of signals which have changed even once from logic 1 to logic 0, N the number of signals which have changed even once from logic 0 to logic 1, and N the number of all signals that are present in the circuit.
To determine a toggle percentage, therefore, it is necessary to have information (changes) of all signals that are present in the LSI circuit. According to the present LSI design approach, the toggle percentage is determined by an RTL simulator.
However, recent digital LSI circuits have been experiencing tremendous multifunctionalization, and the simulating rate has been decreasing steadily. As a result, it has become difficult to determine toggle percentages with RTL simulators. A solution to this problem is a process of determine the toggle percentage by using a hardware simulator. One example of such a hardware simulator is disclosed in JP-A No. 01-026243.